1. Field of the Invention
The present invention relates to an image pickup lens and an image pickup apparatus, and more particularly to an image pickup lens appropriate for use with a vehicle camera, portable terminal camera, surveillance camera, or the like having an image sensor, such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor), and an image pickup apparatus having the image pickup lens.
2. Description of the Related Art
Image sensors, such as CCD or CMOS devices, have recently been greatly downsized with increased pixel counts. Consequently, image pickup devices themselves have also been downsized and image pickup lenses to be mounted on the devices are required to be downsized and improved in performance. In the mean time, lenses used in vehicle cameras and surveillance cameras are required to have a high weather resistance so as to be usable under a sever environment, in addition to be inexpensive and light weighted.
Conventional image pickup lenses with relatively fewer lenses known in the aforementioned fields include, for example, those described in Japanese Unexamined Patent Publication No. 119 (1997)-189856 (Patent Document 1), U.S. Pat. No. 7,760,444 (Patent Document 2), Japanese Patent No. 3756114 (Patent Document 3), and U.S. Pat. No. 7,009,783 (Patent Document 4). Patent Document 1 describes a five lens image pickup lens system in which a first lens on the most object side is a negative meniscus lens with a convex surface oriented to the object side. Patent Documents 2 and 3 describe a four lens image pickup lens system in which a first lens on the most object side is a negative meniscus lens with a convex surface oriented to the object side. Patent Document 4 describes a four lens image pickup lens system in which a first lens on the most object side is a negative meniscus lens with a concave surface oriented to the object side.
In the mean time, requirements for the lenses in the fields described above have been getting strict year after year and the lenses need to satisfy a plurality of sophisticated conditions simultaneously. That is, a compact image pickup lens with fewer lenses, yet having a long back focus to allow a cover glass, filter, and the like to be inserted between the lens system and image sensor, having a small F-number that allows the use of the lens under low illumination, such as during night, ensuring a wide total angle of view of about 60°, and being satisfactorily corrected in aberration, has been sought.
For the image pickup lenses described in Patent Document 1 and Patent Document 2, however, it is difficult to bring forward downsizing while ensuring a long back focus since the power of the first lens on the most object side is small. The image pickup lens described in Patent Document 3 has a large F-number of 3.5 which is inadequate for night time use. The image pickup lens described in Patent Document 4 has a somewhat large F-number of 2.8 and it is difficult to have a wide angle of view because the first lens on the most object side has a negative meniscus shape with a concave surface oriented to the object side.
In view of the circumstances described above, it is an object of the present invention to provide a compact image pickup lens, yet with a long back focus, a wide angle of view, a small F-number, and high optical performance. It is a further object of the present invention to provide an image pickup apparatus having the aforementioned image pickup lens.